TUBES MAN, TUBES!

alright, so i got this amp, its a customized Seymour Duncan 84-40. to me, this amp sounds AMAZING. but its coming time to replace the tubes. i ALWAYS use Groove Tubes Gold Series in my amps but this is my first amp with on-board overdrive. if you are familiar with groove tubes, you know that they go by rating (Low, Medium, or High) and i don't want to buy medium rating and loose all my low end or something like that. so i wanted to know, what rating should i get? the amp as it stands has a real nice marshal tone and i can easily dial in some jimmy page tones and i want to keep it that way.

by the way my amp takes four EL-84's and three 12ax7's

This is where I got my last set of tubes.

http://thetubestore.com/

i know where to get them, i just need to know what rating of tube to get.